The willingness of an individual backed up with purchasing power at a given time is

Analyze the question: The question asks for the term for an individual's willingness to buy, backed up with purchasing power, at a given time.

Explain the concept:

• Want/Desire: a wish for a good or service. It does not need money to support it.
• Utility: the satisfaction gained from consuming a good.
• Demand: the quantity of a good consumers are willing and able to buy at various prices over a period of time.
• Effective demand: the desire for a good that is backed by the ability and willingness to pay (purchasing power) at a given price and time.

Step-by-step solution:

1. "Willingness" alone is only a desire or want, so B and E are ruled out.
2. Utility is satisfaction, not willingness to pay, so D is ruled out.
3. "Backed up with purchasing power" is the key phrase. Economics textbooks use it to define effective demand: a want supported by the money to pay for it.
4. Plain "demand" (A) is close and is often defined as willingness and ability to buy. But it is usually tied to a schedule of prices and quantities.

Answer: C. effective demand

Tip: Remember the formula Effective demand = Desire + Ability to pay (purchasing power). If a question stresses "backed by purchasing power" or "ability to pay", choose effective demand. If it only mentions a wish with no money involved, choose want or desire.